Microinstabilities in the Transition Region of Weak Quasi-perpendicular Intracluster Shocks
Microinstabilities in the Transition Region of Weak Quasi-perpendicular Intracluster Shocks
复制标题
弱准垂直簇内激波过渡区的微观不稳定性
DOI：
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发表时间：
2021
影响因子：
4.9
通讯作者：
Hyesung Kang
中科院分区：
文献类型：
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作者：
Sunjung Kim;J. Ha;D. Ryu;Hyesung Kang
微不稳定性在无碰撞激波的熵产生和粒子加速中起着重要的作用。最近的研究表明，在准垂直（Q）冲击的过渡区，在高β（β = P气体/P B）团簇内介质（ICM）中，反射回旋离子引起的离子温度各向异性可触发Alfvén离子回旋（AIC）不稳定性和离子镜不稳定性，而磁场压缩引起的电子温度各向异性会激发哨声不稳定性和电子镜不稳定性。采用粒子模拟方法（PIC）对音速马赫数为2-3的Q_（10）激波的离子和电子温度各向异性进行了数值估计，并对这些微不稳定性进行了线性稳定性分析。微不稳定性的动力学性质和随后的等离子体波的离子和电子尺度上的广泛的参数范围内，包括β和离子与电子的质量比进行了描述。此外，非线性演化的诱导等离子体波进行检查通过执行二维PIC模拟与周期性边界条件。我们发现，当β = 20-100时，AIC不稳定性在AIC临界马赫数MAIC*<$2.3以上的超临界激波中会诱发离子尺度波并产生激波表面波纹。此外，电子尺度波主要由这些高β激波中的哨声不稳定性产生。由此产生的多尺度波从电子到离子尺度被认为是必不可少的电子注入扩散冲击加速在ICM中的Q波冲击。
Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition region of quasi-perpendicular (Q ⊥) shocks in the high-beta (β = P gas/P B) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfvén ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in the particle-in-cell (PIC) simulations of Q ⊥ shocks with sonic Mach numbers, M s = 2–3, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including β and the ion-to-electron mass ratio. In addition, the nonlinear evolution of the induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for β ≈ 20–100, the AIC instability could induce ion-scale waves and generate shock surface ripples in supercritical shocks above the AIC critical Mach number, MAIC*≈2.3 . Also, electron-scale waves are generated primarily by the whistler instability in these high-β shocks. The resulting multiscale waves from electron to ion scales are thought to be essential in the electron injection to diffusive shock acceleration in Q ⊥ shocks in the ICM.